GB2339763A - Partitioned bag for use as photobioreactor - Google Patents

Description

2339763 PARTITIONED BAG This invention concerns a vessel of transparent

material, which is particularly suited to use as a photobioreactor, but is not limited to such use.

Typically, photobioreactors comprise substantially optically transparent tubes in which photosynthetic organisms, such as algae or the like, dispersed within a culture medium, can utilise light to undergo photosynthetic reactions, so as to grow and multiply. Hitherto, the transparent tubes, which provide conduits for throughflow of the culture medium and dispersed microorganisms, have been made of substantially rigid material, general plastics, arranged in a coiled, fence-like or serpentine configuration. Such configurations may be of considerable size, particularly for commercial scale production of algae, and are expensive to manufacture and maintain. Problems sometimes arise with contamination of the culture medium, e.g. with other microorganisms, which naturally leads to loss of production. Such problems are usually the result of inadequate sterilisation of the tubes prior to use, but since the only means of sterilisation is by flushing with a disinfecting solution, followed by rinsing, it is difficult to ensure that 100% sterility is achieved on all occasions.

Various factors apply when considering the form of a photobioreactor. On the one hand the vessel or conduit should not be too wide or too large as the ratio of the surface area for impingement of light to the volume of the vessel or conduit would be low, and the resulting concentration of algae or the like would be correspondingly low and uneconomic. On the other hand, the vessel or conduit should not be too narrow or too long as the concentration of algae or the like might become too high, resulting in death of the organisms from oxygen poisoning.

The object of the invention is to provide an alternative vessel or system of conduits, suitable for use as a photobioreactor, which is much less expensive to manufacture and maintain than the known vessels/systems, and is less likely to have problems with achieving sterility prior to use.

According to the invention, a vessel, which is particularly suited for use as a photobioreactor, comprises a f lexible bag having front and rear walls, an inlet and an outlet and a plurality of seals formed between the front and rear walls, characterised in that the bag is made of substantially transparent material and in that the seals are so arranged as to provide a plurality of conduits between the inlet and the outlet, a first chamber in communication with the inlet and with each of the conduits, a second chamber in communication with the outlet and with each of the conduits, and a third chamber at a location intermediate the inlet and outlet and in communication with each of the conduits.

Such a vessel would also be suitable for use for any process 3 requiring application of electromagnetic radiation, specifically light, to a liquid or a suspension, for example a process involving a photochemical reaction other than photosynthesis.

Such a vessel could be produced from any suitable transparent plastics, such as polyethylene, polyvinylchloride or polytetrafluoroethylene. It would be very much less expensive to produce and install than a vessel made up of rigid transparent plastics tubing, for example, several hundred percent less expensive. The sealing arrangement could, of course, readily be produced by heat sealing in conventional manner, and methods used for large scale heat sealing around the edges of such bags could be adapted for producing the addition seal(s) defining the conduits.

A further important advantage of such a vessel is that when produced of any of these readily available flexible transparent plastics materials, it could be sterilised by heating in an autoclave prior to use, giving much greater reliability than sterilising by solution, which is the only method available with known photobioreactor conduits. Moreover, after use, disposal of such a bag is a viable alternative to sterilisation for reuse, because of its low cost.

A vessel comprising a flexible bag having front and rear walls, an inlet and an outlet and a plurality of linear seals formed between the front and rear walls is disclosed in GB 2101966 in respect of a container in which a liquid, e.g. blood, may be 4 stored or through which it may be passed while being heated or cooled. However, whilst having the advantages outlined above, the seals in this previous proposal are used to provide, essentially, a single serpentine conduit between the inlet and the outlet.

Small gaps (of 0.24cm) which are left between the ends of some of the seals and the edges of the bag to allow secondary flow from one part of the conduit to another serve to prevent stagnation of the liquid flowing through the bag. They do not provide additional pathways (conduits) through the bag. Nor do they provide chambers which allow intermingling of liquid from respective passageways.

For use in a photobioreactor, a serpentine flow pathway has considerable disadvantages. In particular, as already mentioned, for any given width it cannot be too long or else the build-up of oxygen will kill the photosynthetic algae. It is for this reason that the present invention specifies provision of plural (relatively short) conduits, and chambers adjacent the inlet, the outlet and intermediate these two in which intermixing of fluid from the several conduits can take place. A further purpose of these chambers is to reduce the pressure of flow through the bag which also could damage or kill the photosynthetic organisms if it exceeds a certain level.

In relation to the foregoing points, in preferred embodiments of the vessel of the invention each of the first, second and third chambers preferably has an internal width or diameter at least twice as large as the width or diameter of any one of the conduits.

In most practical embodiments, the sealing arrangement will comprise a plurality of parallel seals, so as to provide plural conduits of equal length. Also, the seals will generally be straight, i.e. rectilinear. However, in principle, it would certainly be possible for the sealing arrangement to comprise non-parallel, e.g. convergent or divergent, seals, and/or curving seal courses. In this respect the use of the term "linear" herein is to be understood in its broadest sense, encompassing both straight (rectilinear) and curving courses, but clearly distinguishing from any arrangement of punctiliform or highly discontinuous seals.

As regards the common problem of adhesion of micro-organisms to the internal surface of conduits during operation of the photobioreactor, cleaning of vessels constructed, in accordance with the invention, of flexible plastics material, can be accomplished in the same manner as described in earlier specification GB 9621130.5, of Biofence Limited, a company associated with the present applicants, by providing mobile beads or a pig within the conduit or conduits and causing these to move to and fro by the introduction and removal of liquid from the vessel, as is normal practice in continuous culture systems.

A specific practical example of a photobioreactor constructed in 6 accordance with the invention will now be described with reference to the accompanying drawing in which the single figure is a schematic side plan view.

As shown, the photobioreactor comprises a flexible bag (10) of substantially optically transparent plastics material, such as polyethylene. The bag (10) may typically be anything from 0.5 to 50m long, and almost as wide. The dimensions will be chosen to suit the site of operation and the scale of production of algae or other photosynthetic organisms that is required.

The bag (10) may be produced in tubular f orm, as is conventional, then pressed f lat and heat sealed at its ends (at 11 and 13), leaving an inlet (12) and an outlet (14) at one end, conveniently adjacent respective corners of the bag (10), as shown. In the illustrated example, additional heat seals (15 and 17) have been effected along both sides of the bag (10).

A less common method of manufacture would involve having separate overlying webs of flexible plastics material, providing front and rear walls of the bag, which are then heat sealed right around their peripheries, again leaving an inlet and an outlet.

A series of parallel heat seals (16, 18, 20) are provided between the front and rear walls of the bag (10). In this embodiment there are seven seals, and they are provided at substantially equal spacings and parallel with the larger sides of the bag (and with the side seals 15, 17). The central seal (20) connects to - 7 the seal (11) which extends between the inlet (12) and the outlet (14), but stops short of the seal (13) at the other end of the bag (10) The ends of the other seals (16 and 18) stop short of, i.e. are spaced from, the seals (11, 13) at the respective ends of the bag (10) Thus, in ef f ect, the seals (16, 18, 2 0) define a first chamber (22) leading from the inlet (12), a second chamber (24) leading to outlet (14), four conduits (26), of substantially equal dimensions, in the upper half of the bag, four conduits (28), also of substantially equal dimension, in the lower half of the bag, and an intermediate chamber (30), where all the conduits (26, 28) are in communication, adjacent the end of the bag remote from the inlet (12) and the outlet (14). These chambers (22, 24, 30) have a function corresponding to that of manifolds in an equivalent fence-like arrangement of conduits made of separate tubes. The chamber (30) is, of course, half way along the flow path between the inlet (12) and the outlet (14).

In this specific illustrated example, the chambers (22, 24, 30) may each have a diameter, when filled, of about 5cm. In other words, the gaps between the ends of the seals (16, 18) and the edge seals (11, 13) and also the gap between the end of the seal (20) and the edge seal (13) is about 5cm. The distance between the adjacent seals (16, 18, 20) is only about 2.2cm, which is therefore the approximate width or diameter of the conduits (26, 28). Thus the chambers (22, 24, 30) are more than twice the width/diameter of the conduits (26, 28).

In a somewhat larger version of photobioreactor, the width of the - 8 chambers (22, 24, 30) may be about 7cm, and that of the conduits (26, 28) about 2.8cm, giving a ratio of 2.25:1.

When the bag (10) is used as a photobioreactor, it may advantageously be supported in a vertical disposition, just as illustrated, as this minimises f loor space requirements and will usually maximise the area in receipt of incident sunlight. Liquid culture medium with a chosen strain of algae suspended therein will be circulated through the bag. Preferably the inlet (12) will be at the bottom, the outlet (14) at the top, so that the liquid f lows to the right along the conduits (28) in the bottom half of the bag (10), as shown in the drawing, and then to the left along the conduits (26) in the top half of the bag (10). The rate of flow will generally be of the order of 0.5 to I.Om/s or less, and this will typically be maintained by a pump located in a pipe leading to the inlet (12). Between the outlet (14) and the inlet (12), the liquid will pass into a collection vessel, from where a certain proportion of the algae may be harvested, e.g. by filtration and/or sedimentation, with the extracted volume replenished by fresh culture medium. With the outlet (14) at the top, the liquid may be allowed to drop or splash into the collection vessel, which results in bubble formation and aids the purging of oxygen therefrom.

The dimensions of the conduits (26, 28), i.e. the arrangement of the seals (16, 18, 20) will be chosen depending on the strain of micro- organism being cultured, and other factors, such as the flow rate, light intensity, etc.

The provision of the chambers (22, 24, 30) is important in countering build up of a high oxygen concentration in any one of the conduits (26, 28) which could lead to failure of the whole system by poisoning, and also in minimising the pressure head. The overall arrangement provides a large surface area/volume ratio for incident light, and a short residence time, as the culture medium passes relatively quickly from the inlet to the outlet.

The flexible plastics bag (10) provides the required conduit system of the photobioreactor in a particularly compact and cost effective manner, and has the advantage of being able to withstand autoclaving, so that it can be reliably sterilised prior to use.

Numerous variations in the sealing arrangements, the number and arrangement of the conduits and other details are, of course, possible within the scope of the invention. Although the illustrated arrangement of conduits, with a chamber for communication provided at the opposite end to the inlet and outlet is particularly favourable because it is compact, a larger bag could be provided with an inlet and an outlet at opposite ends and a communication chamber midway between these. Other embodiments may include several communication chambers at appropriate intervals.

Claims (6)

1. A vessel comprising a flexible bag having front and rear walls, an inlet and an outlet and a plurality of linear seals formed between the front and rear walls, characterised in that the bag is made of substantially transparent material and in that the seals are so arranged as to provide a plurality of conduits between the inlet and the outlet, a first chamber in communication with the inlet and with each of the conduits, a second chamber in communication with the outlet and with each of the conduitst and a third chamber at a location intermediate the inlet and outlet and in communication with each of the conduits.

2. A vessel according to claim 1 wherein each of the first, second and third chambers has an internal width or diameter at least twice as large as the width or diameter of any one of the conduits.

3. A vessel according to claim 1 or 2 wherein the inlet and the outlet and the respective first and second chambers are disposed at one end of the bag and the third chamber is disposed at the opposing end of the bag.

4. A vessel according to claim 1, 2 or 3 wherein the arrangement of linear sealing between the front and rear walls of the bag consists of or includes a plurality of parallel seals.

5. A vessel according to any preceding claim wherein the linear course of the or each seal between the front and rear walls is straight.

6. A vessel in the form of a flexible bag having a plurality of conduits formed between an inlet and an outlet substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.